1. Field of the Invention
This invention relates to scroll compressors installed in air conditioners, refrigerators and the like.
2. Description of the Related Art
Scroll compressors are composed of fixed scroll members and revolving scroll members (i.e., pairs of scroll members) whose centrifugal walls (or spiral walls) are arranged in engagement with each other and which are subjected to revolving motions. That is, the scroll compressor operates in such a way that the revolving scroll member revolves with respect to the fixed scroll member. Thus, it performs fluid compression of its compression space, which is formed between the walls of the scroll members, and is gradually reduced in volume during compression.
FIGS. 7A and 7B show a pair of scroll members that are installed in the conventional scroll compressor described above. FIG. 8 is a plan view diagrammatically showing a center portion of a centrifugal wall of a scroll member, which is installed in the scroll compressor disclosed in Japanese Unexamined Patent Publication No. Sho 59-58187. FIGS. 9A and 9B diagrammatically show a center portion of a centrifugal wall of a scroll member, which is installed in the scroll compressor disclosed in Japanese Unexamined Patent Publication No. Hei 9-68177. FIG. 10 is a plan view diagrammatically showing a center portion of a centrifugal wall of a scroll member, which is installed in the scroll compressor disclosed in Japanese Unexamined Patent Publication No. Hei 10-68392.
Operations of the aforementioned scroll compressors having paired scroll members will be discussed below.
A first example of the scroll compressor has a combination of a fixed scroll member 1 shown in FIG. 7A in which a centrifugal wall 1b is arranged on an end board 1a, and a revolving scroll member 2 shown in FIG. 7B in which a centrifugal wall 2b is arranged on an end board 2a. These scroll members 1 and 2 are combined together in such a way that the centrifugal walls 1b and 2b engage with each other and are shifted from each other with a certain angle of dislocation, which is about 180 degrees (180xc2x0). In the engaged state of the scroll members, the revolving scroll member 2 is revolved so that a closed space being formed between the centrifugal walls 1b and 2b moves inwardly from its outer position to its inner position while being gradually reduced in volume. Thus, it is possible to perform fluid compression in the compression space.
The closed space located in its innermost position bears a high pressure, whereas the closed space located in its outer position becomes low in pressure. This causes reaction of compressed gas in the center portion of the centrifugal walls 1b and 2b combined together. Repeatedly revolving the scroll member 2 causes repetition of the reaction of the compressed gas being effected in the center portions of the centrifugal walls 1b and 2b. The center portions also correspond to spiral-starting portions of the centrifugal walls 1b and 2b, which bear shortage of rigidity. Therefore, fatigue failure may occur at root portions at which the centrifugal walls 1b and 2b are respectively affixed to the end boards 1a and 2a. 
A second example of the scroll compressor disclosed in Japanese Unexamined Patent Publication No. Sho 59-58187 is provided to solve the aforementioned problem, which will be described with reference to FIG. 8.
FIG. 8 shows a center portion (or a spiral-starting portion) of a centrifugal wall 3 of the scroll member installed in the scroll compressor, wherein involute curves are drawn with respect to an exterior and an interior of the centrifugal wall 3 respectively. A first position is fixed at a certain involute angle xcex1 on the first involute curve corresponding to the exterior of the centrifugal wall 3, while a second position is fixed at an involute angle (xcex1+180xc2x0) on the second involute curve corresponding to the interior of the centrifugal wall 3. In addition, a small circular arc is drawn with respect to the first position on the first involute curve, while a large circular arc is drawn with respect to the second position on the second involute curve. Hence, the center portion of the centrifugal wall 3 is formed by connecting the involute curves with the circular arcs. Thus, it is possible to increase the thickness of the centrifugal wall 3 at its center portion, which yields an improvement in strength. However, the aforementioned technique does not provide sufficient improvement in rigidity because a high concentration of stress still remains in proximity to the small circular arc of the center portion of the centrifugal wall 3.
A third example of the scroll compressor disclosed in Japanese Unexamined Patent Publication No. Hei 9-68177 provides a further improvement in rigidity, which will be described with reference to FIGS. 9A and 9B.
That is, it is characterized by providing stepped wall surface portions for both of the fixed and revolving scroll members. FIGS. 9A and 9B show a centrifugal wall 4 installed in the scroll compressor, wherein a stepped wall surface portion is formed between a first position, which is fixed at a certain involute angle xcex1 on an involute curve corresponding to an exterior of the centrifugal wall 4, and a second position which is fixed at an involute angle (xcex1+180xc2x0) on an involute curve corresponding to an interior of the centrifugal wall 4. A closed space is defined as a combination of a spiral-inside closed space and a spiral-back-side closed space being formed between the centrifugal walls of the scroll members combined together, and its volume changes in response to engaged states of the scroll members. The center portions of the centrifugal walls of the scroll members combined together are shaped to establish a profile of complete engagement in which the volume of the closed space at its innermost position becomes substantially zero. In addition, the thickness of the stepped wall surface portion of the centrifugal wall 4 is changed in such a step-by-step manner that the thickness is gradually reduced upwards from the end board. Due to the provision of the stepped wall surface portion for the center portion of the centrifugal wall, it is possible to selectively increase the thickness of the center portion of the centrifugal wall at its root portion only. This allows a further improvement in the strength of the scroll member installed in the scroll compressor.
A fourth example of the scroll compressor disclosed in Japanese Unexamined Patent Publication No. Hei 10-68392 will be described with reference to FIG. 10. FIG. 10 shows a centrifugal wall 5 of the scroll member whose center portion has a stepped wall surface portion. In addition, the center portion of the centrifugal wall 5 is partially shaped to allow provision of a root fillet 5a in a certain area defined between connection points of spiral curves and circular arcs drawn for the exterior and interior of the centrifugal wall 5. Similarly, a root fillet (not shown) is also provided for another centrifugal wall 6 that engages with the centrifugal wall 5. In order to avoid interference between the root fillets of the centrifugal walls 5 and 6, a gap is provided therebetween in a wall thickness direction. This reduces concentration of stress at the root portion of the centrifugal wall. Therefore, it is possible to further improve the strength of the scroll member.
The third example of the scroll compressor shown in FIGS. 9A and 9B bears the following problems. The closed space formed between the centrifugal wall of the fixed scroll member and the centrifugal wall of the revolving scroll member has a dead volume at a last step of compression. The dead volume corresponds to the volume of the xe2x80x98innermostxe2x80x99 closed space that is established at a seal-off point, at which the innermost closed space communicates with a second closed space having a crescent shape that is located one lap outside from the innermost closed space. As the dead volume becomes larger, high-pressure gas is subjected to re-expansion, which will cause reduction of the compression efficiency of the scroll compressor.
The aforementioned seal-off point is defined substantially at the moment when the centrifugal walls of the paired scroll members separate from each other or at the moment when the exterior of the centrifugal wall comes into contact with the discharge port (not shown) that is arranged in proximity to the center portion of the end board. Normally, the scroll compressor locates the discharge port on the end board of the fixed scroll member. In addition, the discharge port is located at the position that does not cause problems in the strength of the centrifugal wall of the fixed scroll member and is arranged in proximity to the spiral-inside of the center portion of the centrifugal wall such that the seal-off point emerges at the last step of compression as possible. In order to improve performance of the scroll compressor by reducing the dead volume, it is necessary to maintain the innermost closed space sealed as tightly as possible. Therefore, the optimal engagement of the centrifugal walls of the paired scroll members should be secured substantially at the moment when the centrifugal wall of the revolving scroll member comes into contact with the discharge port, which is located in proximity to the center portion of the end board of the fixed scroll member.
The third example of the scroll compressor shown in FIGS. 9A and 9B is designed such that the stepped wall surface portion is formed on the center portion of the centrifugal wall in order to improve its strength. This increases the number of sealed locations due to new addition of engaging portions that appear between stepped wall surface portions of the centrifugal walls of the paired scroll members in their height directions. Such newly sealed locations should be subjected to slide-contact sealing. This increases dimensions that should be managed in machining of scroll members, which causes an increase in the manufacturing cost. Incomplete sealing causes a leakage of gas from the innermost closed space, which causes a problem that the compression efficiency is reduced.
The fourth example of the scroll compressor shown in FIG. 10 sets engaged portions of centrifugal walls of paired scroll members along with involute curves of the centrifugal walls at the aforementioned seal-off points that depend on the position of the discharge port. For this reason, the fourth example does not cause the foregoing problem of the third example because it secures easy sealing between centrifugal walls. Even in the fourth example of the scroll compressor, the discharge port is located at the prescribed position by which the seal-off points emerge at the last step of compression. Generally speaking, the engaged portions of the centrifugal walls of the paired scroll members frequently emerge along involute curves corresponding to interiors of the centrifugal walls at the seal-off points that are directly determined by the position of the discharge port. Therefore, the fourth example also increases the number of sealed locations due to new addition of engaging portions that appear between stepped wall surface portions of the centrifugal walls of the paired scroll members in their height directions. Such newly sealed locations should be subjected to slide-contact sealing. This increases dimensions that should be managed in machining of scroll members, which causes an increase in the manufacturing cost. Incomplete sealing causes a leakage of gas from the innermost closed space, which causes a problem in that the compression efficiency is reduced.
The aforementioned third example of the scroll compressor shown in FIGS. 9A and 9B is designed to improve the strength by increasing the thickness of the root portion of the centrifugal wall at its center, spiral-starting portion. If the centrifugal wall does not have the stepped portion, the discharge port 5 can be positioned in proximity to the interior of the centrifugal wall, which is shown in FIG. 11A. However, if the centrifugal wall has the stepped portion, the discharge port 5 should be located far from the centrifugal wall, which is shown in FIG. 11B. This increases the dead volume of the closed space formed between the centrifugal walls engaging with each other at the seal-off points, which depend upon the position of the discharge port. Therefore, the third example of the scroll compressor suffers from a problem in that the compression efficiency is reduced due to the formation of the stepped portion along the interior of the centrifugal wall in proximity to the discharge port of the fixed scroll member.
It is an object of the invention to provide a scroll compressor in which centrifugal walls of scroll members have high strength and which allows easy machining of scroll members.
It is another object of the invention to provide a scroll compressor that does not cause unwanted reduction of the compression efficiency by minimizing dead volume of closed spaces formed between centrifugal walls of scroll members engaging with each other.
Specifically, this invention provides a scroll compressor that comprises a fixed scroll member having a centrifugal wall planted on its end board, a revolving scroll member having a centrifugal wall planted on its end board, wherein these scroll members are combined together in such a manner that their centrifugal walls engage with each other. In addition, a rotation stop mechanism supports the revolving scroll member to revolve with respect to the fixed scroll member while preventing the revolving scroll member from performing self-rotation.
In a first aspect of this invention, each of the centrifugal walls of the paired scroll members is designed in plan in consideration of involute starting points xcex21 and xcex22 for respectively starting the exterior and interior of the spiral-starting portion, and seal-off points xcex21xe2x80x2 and xcex22xe2x80x2 that are set between the involute starting points xcex21 and xcex22, by which the centrifugal walls separate from each other due to revolution of the revolving scroll member. In addition, the spiral-starting portion designed for each of the centrifugal walls comprises non-stepped portions formed in respective areas of xcex21-xcex21xe2x80x2 and xcex22-xcex22xe2x80x2 in which the centrifugal wall has constant thickness in its height direction, and a stepped portion formed in at least a part of an area xcex21xe2x80x2-xcex22xe2x80x2 in which the thickness of the centrifugal wall is changed in such a stepped manner that its lower side is increased in thickness as compared with its upper side. Herein, the centrifugal walls of the paired scroll members engage with each other at their first and second non-stepped portions.
In the above, the non-stepped portions are formed by a first curve xcex21-xcex21xe2x80x2 and a second curve xcex22-xcex22xe2x80x2 respectively, whereas the lower side of the stepped portion is formed by third and fourth curves smoothly connected between the points xcex21xe2x80x2 and xcex22xe2x80x2, and the upper side of the stepped portion is formed by fifth and sixth curves smoothly connected between the points xcex21xe2x80x2 and xcex22xe2x80x2. In addition, a first compression space (C1) is formed between the centrifugal walls of the paired scroll members at their innermost position and communicates with a discharge port formed at the center of the end board of the fixed scroll member due to revolution of the revolving scroll member, and a second compression space (C2) is also formed outside of the first compression space. Further, the seal-off points xcex21xe2x80x2 and xcex22xe2x80x2 substantially match engaging points of the centrifugal walls being established just before the second compression space moves to communicate with the discharge port during revolution of the revolving scroll member.
In a second aspect of this invention, each of the centrifugal walls of the paired scroll members provides a stepped portion in its spiral-starting portion, in which the thickness of the centrifugal wall is changed in a stepped manner such that its lower side is increased in thickness compared to its upper side, so that the stepped portion of the centrifugal wall in plan view is increased in thickness within a thickness increase area (N) encompassed by an upper-side curve representing a curved surface of the upper side of the stepped portion and a lower-side curve representing a curved surface of the lower side of the stepped portion. In addition, the discharge port is located to partly overlap with the thickness increase area by approximately a half portion. Further, the lower side of the stepped portion is partly hollowed to accommodate approximately the half portion of the discharge port so that a hollowed portion is formed to encroach into the thickness increase area in plan view, wherein the hollowed portion is enlarged in the height direction of the stepped portion with the prescribed height (h), which is determined to secure an opening area substantially matching a flow passage sectional area of the discharge port.